There are three major aims of the proposed research. The first is to provide an objective comparison of different forms of periodontal therapy, in terms of plaque and tissue response, as well as maintenance level of attachment. The second is to provide the clinician with guide-lines as to which forms of therapy are most appropriate for different forms of periodontal disease. The third is to evaluate the periodontal pocket microbiota and histologically the response of tissues in sites in which periodontal therapy fails and recurrent disease develops. The periodontal conditions of a group of patients who in 1978 - 1979 were subjected to either one non-surgical and one surgical method of periodontal therapy as well as periodontosis patients treated by surgical and antibiotic therapy will be monitored for another 3 years. In these patients some clinical microbiolgical and histopathological characteristics of peridontal sites which show recurrence of periodontal disease will be analyzed. In addition, in a new set of patients "critical probing depth", i.e. probing depths at various tooth surfaces below which loss of clinical attachment results following gingivectomy and flap procedures.